A socket, which is illustrated in FIGS. 11A through 12B (see JP2005-209617A), for example, is well known as a pin grid array (PGA) integrated circuit (IC) socket. FIGS. 11A and 11B show the conventional PGA IC socket; FIG. 11A is a sectional view of a PGA IC socket before the slide cover is moved, and FIG. 11B is a sectional view of the PGA IC socket after the slide cover is moved. FIGS. 12A and 12B show the socket contact; FIG. 12A is a left side view, and FIG. 12B is a front view.
The PGA IC socket (hereinafter referred to simply as “socket”) 101, shown in FIGS. 11A and 11B, includes numerous socket contacts 120 that respectively contact numerous lead pins 151 of an IC package 150, a thin plate-form housing 110 in which contact cavities 111 that respectively accommodate the socket contacts 120 are arranged in a two-dimensional array, and a slide cover 130 which is provided on the upper portion of the housing 110 so as to be movable in a forward-backward direction (left-right direction in FIG. 11A).
As is shown in FIGS. 11A through 12B, each of the socket contacts 120 include a substantially rectangular plate-form retention section 121 that is press-fit into one of the contact cavities 111 of the housing 110, an resilient contact part 124 that extends from the upper end of the retention section 121, and a foot 126 that is provided at the lower end of the retention section 121. Upper engaging projections 121a and lower engaging projections 121b, which are press-fit into the corresponding contact cavity 111, are provided at both edge portions of the retention section 121 as shown in FIGS. 12A and 12B. The retention section 121 is press-fit into the contact cavity 111 such that the rear surface side (the back surface side with respect to the plane of page in FIG. 12B and the left surface side in FIG. 11A) of the retention section 121 follows along the side wall surface 111a that is on the rear side (left side in FIG. 11A) out of the side wall surfaces that partition the contact cavity 111 as shown in FIGS. 11A and 11B. Furthermore, the resilient contact part 124 includes a substantially rectangular plate-form base section 123 that extends in the direction of width of the retention section 121 (in the left-right direction in FIG. 12B and in a direction orthogonal to the plane of page in FIG. 11A) from the upper end edge of the retention section 121 via a narrowed part 122, and a pair of resilient contact pieces 125 that first extend forward (toward the viewer with respect to the plane of page in FIG. 12B and rightward in FIG. 11A) from either end of the base section 123 and then extend upward. The paired resilient contact pieces 125 are inclined in such a way to approach each other toward the tip ends thereof, and a lead pin 151 provided on the IC package 150 contacts between these resilient contact pieces 125. Moreover, the foot 126 extends forward from the lower end of the retention section 121, and a solder ball 127 is formed on the undersurface of the foot 126.
In cases where the IC package 150 is attached to the socket 101 shown in FIGS. 11A and 11B, the lead pins 151 are first respectively inserted into the contact cavities 111 by passing through receiving passageways 131 formed in the slide cover 130. Next, when the slide cover 130 is caused to move forward (in the arrow direction in FIG. 11A) by operating a lever or the like (not shown in the figures), a state is created in which the lead pins 151 are respectively held between the paired resilient contact pieces 125 of the socket contacts 120 as shown in FIG. 11B, thus making contact with these resilient contact pieces 125. As a result, the lead pins 151 and the corresponding solder balls (a circuit board connected to the solder balls) 127 are electrically connected. Here, the length L from the tip end of each lead pin 151 to the corresponding resilient contact pieces 125 contacted by the lead pin 151 is called an effective mating length.
In addition, the socket shown in FIGS. 14 and 15 (see JP2001-43940A), for instance, has also been known as another example of a conventional PGA IC socket. FIG. 14 is an explanatory diagram showing the relationship between a socket contact and a lead pin inside the housing in another example of a conventional PGA IC socket. FIG. 15 is a perspective view of a socket contact used in the PGA IC socket shown in FIG. 14.
The PGA IC socket (hereinafter referred to simply as “socket”) 201 shown in FIG. 14 includes numerous socket contacts 220 that respectively contact numerous lead pins 251 of an IC package (not shown in the figures), a housing 210 in which contact cavities 211 that respectively accommodate the socket contacts 220 are arranged in a two-dimensional array, and a slide cover 230 which is provided on the upper portion of the housing 210 so as to be movable in the forward direction (direction of arrow F in FIG. 14) and in the backward direction (direction of arrow B in FIG. 14).
As is shown in FIGS. 14 and 15, each of the socket contacts 220 includes a substantially rectangular plate-form base section 221 that is press-fit in the bottom wall 212 of one of the contact cavities 211 of the housing 210, a substantially rectangular plate-form supporting section 222 that extends upward from the upper edge of the base section 221 and that has a smaller width than the base section 221, and a pair of resilient contact pieces 223 that extend from either side edge at the lower end of the supporting section 222. The base section 221 is press-fit in the bottom wall 212 of the corresponding contact cavity 211 such that the front surface side of the supporting section 222 follows along the side wall surface 211a that is on the front side out of the side wall surfaces which partition the contact cavity 211. A solder ball 228 is formed at the lower end of the base section 221. Furthermore, the resilient contact pieces 223 respectively include holding sections 224 that extend backward from the side edges at the lower end of the supporting section 222, introduction sections 225 that are provided at the tip ends of the holding sections 224, and pressing sections 226 that extend from the introduction sections 225 toward the supporting section 222; each of the resilient contact pieces 223 is formed substantially in the shape of the letter U. Legs 227 that slide over the bottom wall 212 when the resilient contact pieces 223 move are respectively provided at the lower ends of the introduction sections 225.
In cases where an IC package is attached to the socket 201 shown in FIG. 14, the lead pins 251 are first respectively inserted into the contact cavities 211 by passing through receiving passageways 231 formed in the slide cover 230. In this case, the tip end of each lead pin 251 is positioned between the introduction sections 225 of the corresponding socket contact 220. Next, when the slide cover 230 is caused to move forward by operating a lever or the like (not shown in the figures), a state is created in which the lead pins 251 are held between the paired pressing sections 226 of the corresponding socket contacts 220, thus making contact with the resilient contact pieces 223. As a result, the lead pins 251 and the corresponding solder balls (a circuit board connected to the solder balls) 228 are electrically connected.
However, in these sockets 101 and 201, there are cases in which the sockets 101 and 201 become warped in a concave shape as shown in FIG. 13 (only the socket 101 is shown in FIG. 13). In a case in which the socket 101 shown in FIGS. 11A and 11B is warped in a concave shape, for example, if the effective mating length L is short, the lead pins 151 provided on the IC package 150 do not contact the socket contacts 120 in some instances. For this reason, it is desirable to set the effective mating length L long in the sockets 101 and 201.
Meanwhile, with the sockets 101 and 201, as a result of electronic devices becoming higher in performance and smaller in size, there has been a demand for the socket contacts 120 and 220 to be arranged with a higher density and for the sockets 101 and 201 themselves to become lower in height.
Here, in the case of the socket 101 shown in FIGS. 11A and 11B, when the lead pins 151 are respectively inserted into the contact cavities 111 by passing through the receiving passageways 131 formed in the slide cover 130, these lead pins 151 are positioned directly above the retention section 121 of the corresponding socket contacts 120 attached to the housing 110. Therefore, if an attempt is made to reduce the height of the socket 101 while keeping the effective mating length L long, there is a danger of the tip ends of the lead pins 151 and the upper ends of the retention section 121 contacting each other. Thus, in the case of the socket 101 shown in FIGS. 11A and 11B, there is a limit to the height reduction.
In the case of the socket 101 shown in FIGS. 11A and 11B, furthermore, the resilient contact pieces 125 with which the lead pins 151 make contact respectively extend from both ends of the base section 123 that respectively extend in the direction of width of the retention section 121 from the upper end edges of the retention section 121 via the narrowed parts 122. Therefore, there is a drawback in that the spring length of the resilient contact pieces 125 is short compared to the case of the resilient contact pieces 125 respectively extending from the lower portions of the retention section 121.
Moreover, in the case of the socket 101 shown in FIGS. 11A and 11B, the retention section 121 are press-fit toward the bottom of the contact cavities 111 that pass through the housing 110 in the vertical direction as shown in FIG. 11A. When the retention section 121 of the socket contacts 120 are thus press-fit toward the bottom of the contact cavities 111, the lower side of the housing 110 is deformed, so that the lower side of the housing 110 becomes warped in a concave shape (as shown in FIG. 13) with respect to a printed circuit board (PCB) on which the socket 101 is mounted.
Meanwhile, in the case of the socket 201 shown in FIG. 14, when the lead pins 251 are respectively inserted into the contact cavities 211 by passing through the receiving passageways 231 formed in the slide cover 230, the tip ends of the lead pins 251 are positioned between the introduction sections 225 of the corresponding socket contacts 220, and are not positioned directly above the base sections 221. Furthermore, even in cases where the slide cover 230 moves forward to create a state in which the lead pins 251 are held between the paired pressing sections 226 of the corresponding socket contacts 220, the tip ends of the lead pins 251 are not positioned directly above the base section 221. Accordingly, even if an attempt is made to reduce the height of the IC socket 201 while keeping the effective mating length long, there is no risk of the lead pins 251 and the upper ends of the bottom wall 212 contacting each other, so that the height reduction of the socket 201 can be achieved.
However, even in the socket 201 shown in FIG. 14, because the resilient contact pieces 223 respectively extend from the side edges at the lower ends of the supporting section 222, i.e., the upper edges of the base section 221, there is a drawback in that the spring length of the resilient contact pieces 223 is short compared to the case of the resilient contact pieces 223 extending from the lower portions of the base section 221.
In addition, in the case of the socket 201 shown in FIG. 14, the base sections 221 are respectively press-fit in the bottom walls 212 of the contact cavities 211. Therefore, in the case of the socket 201 as well, when the base section 221 are respectively press-fit in the bottom walls 212, the lower side of the housing 210 is deformed, creating a problem in that the lower side of the housing 210 becomes warped in a concave shape with respect to the circuit board (not shown in the figures) on which the socket 201 is mounted.